We use microsoft graph api to integrate people's mailbox with our application and also send email form our application as their outlook behalf.
The problem is some of our users cannot send the email through our application(which used microsoft API). They get a bouncing email saying "550 5.7.708 Service unavailable Access denied" Traffic not accepted from this IP. (See the attached image)
But the error only happens only when they send emails through GraphAPI, when they send email to the same person on Outlook it works flawlessly.
I noticed some people having the same problem here: and their solution is to contact microsoft. But I don't know where to get technical support when we don't have azure support subscription. I hope some microsoft staff will find this thread and advice us on how to proceed.
This is affecting our business badly. If anyone can guide us it would be much appreciated